Treating manganese-containing ores with a metal sulfide

ABSTRACT

A process for treating a first metal, manganese-containing ore comprising contacting the manganese-containing ore with an aqueous, acidic composition and a material containing at least one metal sulfide at conditions effective to (1) chemically reduce at least a portion of the manganese, (2) solubilize at least a portion of the metal from the metal sulfide, and (3) at least partially liberate the first metal from the ore; and recovering the first metal from the ore. The use of Thiobacillus ferrooxidans and/or added ferric ion in the contacting step are also disclosed.

This application is a continuation-in-part of co-pending application Ser. Nos. 687,675; 687,677; and 687,672; all filed on Dec. 31, 1984 and all now abandoned.

This invention relates to a process for recovering at least one first metal, e.g., silver, from a ore containing reducible manganese and the first metal. In particular, the invention relates to a process for recovering the first metal which involves processing the first metal, reducible manganese-containing ore so as to facilitate the recovery of the first metal from the ore.

Reducible manganese-containing ores quite often contain metal values which are difficult to recover because of the "locking" nature of the manganese in the ore. For example, the occurrence of manganese-locked silver ores has long been a problem for ore processors. Conventional smelting can treat small, limited quantities of manganese-locked silver ores when processing conventional ores. The manganese must be properly slagged to prevent attack of the crucibles. This consumes silica, increases energy required, and contributes to metal loss in the slag. Manganese-locked silver ores may be leached with sodium cyanide to recover silver, but such recovery is often limited by the manganese content. Manganese in such ores "locks" the silver in the ore by, for example, blocking access by the sodium cyanide solution to the silver minerals.

Use of sodium cyanide to remove silver from such manganese-locked silver ores is usually uneconomical. Moreover, stringent air pollution control regulations and low metal prices have forced smelters to shut down or select ores from which metal values can be recovered relatively easily. Ores which include "locking" manganese (e.g., containing about 0.5% to about 35% by weight of manganese) are often considered marginal and may not be processed.

One known process for recovering silver from silver, manganese-containing ores is disclosed in "Wringing Manganese from Silver Ores", Chemical Week (Dec. 14, 1983), 30, 32. In this article, a process is described in which a proprietary leaching solution is applied to a silver, manganese-containing ore which is agitated at ambient temperatures. In the first stage, manganese is dissolved and treated with a metal carbonate. In the second stage, silver is dissolved and finally recovered by electrowinning. The leaching solution which is used for dissolving the manganese, as well as the leaching solution used to dissolve the silver, were disclosed as being proprietary.

One method to improve the cyanide extraction of silver from a silver, manganese-containing ore is disclosed in an article entitled "Cyanide Milling Practice of The Fresnillo Company", W. E. Crawford, Tran. AIME 112 (1934), 734-750. This method involves (1) grinding the ore in water to form a pulp; (2) subjecting the pulp to sulfur dioxide gas to dissolve the manganese minerals; (3) precipitating the dissolved manganese with a lime emulsion; (4) aerating the pulp; and, finally (5) cyaniding the pulp in the usual manner to recover the silver values. The article teaches that the manganese as such no longer adversely affects silver extraction, although it still remains in the pulp.

U.S. Pat. No. 2,829,964 (hereinafter referred to as '964) describes a process for leaching metals (mainly copper and iron) from metallurgical materials with a leaching agent containing ferric sulfate and sulfuric acid. This leaching process uses ferric sulfate to convert the metal to be recovered to a soluble form and produces a spent solution containing ferrous sulfate. In a separate regenerative stage, bacteria named Thiobacillus ferrooxidans act on the spent ferrous sulfate to oxidize it to form the necessary ferric sulfate which is recycled back to the leaching step. The bacteria may also act on iron pyrite which is optionally present in the separate regeneration step to generate the ferric sulfate leaching agent.

U.S. Pat. No. 3,433,629 (hereinafter referred to as '629) discloses a process for dissolving and recovering manganese from manganese (IV) dioxide-containing ore. The process includes the steps of adding powdered manganese dioxide-containing ore and a metal sulfide to a cultured liquid containing Thiobacillus thiooxidans bacteria. The '629 patent makes clear that the process utilizing Thiobacillus thiooxidans is based on entirely different functions from the process of the '964 patent which involves a ferric sulfate leaching agent and a separate regeneration stage utilizing Thiobacillus ferrooxidans. Further, the '629 patent questions the use of the 3 964 process with manganese-containing ores since both manganese dioxide (MnO₂) and ferric sulfate are of an oxidized nature. Therefore, the ferric sulfate in the leaching agent can never be reduced to the ferrous state as taught by the '964 patent. Example 3 of '629 discloses that the use of FeS, in the absence of the Thiobacillus thiooxidans bacteria, to dissolve manganese dioxide gave poor results.

One major disadvantage of the '629 process is the necessity to continuously supply sulfur or sulfur dioxide to the site of bacterial action. Further, the alternative suggested in '629 of mixing the ore with a nonionic surfactant is also expensive and troublesome. The process also requires the use of a large excess of sulfuric acid for maintenance of the pH in the range of about 0.5 to about 1.0. This aspect, besides increasing the initial raw material cost, requires high neutralization costs prior to the recovery of silver using cyanide.

U.S. Pat. No. 4,002,717 (hereinafter referred to as '717) discloses a method for obtaining soluble manganese salt from a high valence manganese oxide ore without solubilizing iron (from iron sulfide) and simultaneously, if desired, refining a metal (iron) sulfide ore. The '717 process involves admixing the manganese oxide ore with hydrogen sulfide or metal sulfide and sulfuric acid to form elemental sulfur and an aqueous leach solution comprising dissolved manganese sulfate. The '717 patent teaches that compounds which are polysulfides, i.e., those that contain an S-S bond, for example such as that present in iron pyrites, are inert in the '717 process.

Other U.S. patents and literature references which were reviewed in preparing this application are as follows: U.S. Pat. Nos.: 4,497,778; 3,330,650 and 3,169,856; and literature reference: Tuovinen, O. H., and Kelly, D. P., "Use of Microorganisms for the Recovery of Metals", International Metallurgical Reviews, Vol. 19, 1974, pgs. 21-31. Also see commonly assigned U.S. patent application Ser. No. 858,369, the specification of which is hereby incorporated by reference herein. There continues to be a need for improved processing to recover metal values from reducible manganese-containing ores.

Therefore, one object of the present invention is to provide a process for recovering at least one other metal from a reducible manganese-containing ore.

Another object of the invention is to provide such a process utilizing pyrites, and particularly iron pyrites, as ores and minerals.

A further object of the invention is to provide a process for the recovery of silver from a silver, reducible manganese-containing ore.

A still further object of the invention is to provide a process for the recovery of at least one other metal from a reducible manganese-containing ore utilizing certain bacteria. Other objects and advantages of the present invention will become apparent hereinafter.

An improved process for recovering at least one first metal other than manganese from an ore containing reducible manganese, e.g., manganese generally in the plus four (+4) oxidation state, has been discovered. In one broad aspect, the process comprises: contacting the ore with an aqueous, acidic composition and a material, e.g., a metallurgical material, ore and the like, containing at least one metal sulfide at conditions effective to (1) chemically reduce at least a portion of the manganese, (2) solubilize at least a portion of the metal from the metal sulfide in the acidic, aqueous composition, and (3) at least partially liberate the first metal from the ore; and recovering the first metal from the ore. In one embodiment, the metal sulfide has a formula of (Me)ySx wherein x is greater than y and Me is a metal selected for the group consisting of Fe, Mo, As, Cu, Co, Ni, Sn, Sb, Bi, Pb, Zn and mixtures thereof. Such metal sulfides preferably include at least one S-S (sulfur to sulfur) bond. Such sulfides include iron pyrites and pyrite-like metal sulfides. In another embodiment, the contacting occurs in the presence of Thiobacillus ferrooxidans in an amount effective to facilitate, e.g., generally to increase the rate of, the liberating of the first metal or metals from the ore. These two embodiments are meant to be inclusive and not exclusive. That is, the (Me)ySx of the first embodiment may be used in conjunction with the Thiobacillus ferrooxidans of the second embodiment.

The present process provides substantial advantages. For example, relatively inexpensive metal sulfides, in particular iron pyrites, may be used. At least partial liberation of the first metal, in particular silver, is achieved, thereby providing for an effective, e.g., increased metal yield and/or reduced cost, metal recovery step. In addition, since at least a portion of the metal from the metal sulfide is solubilized, the present process can be utilized to recover at least one second metal, in particular selected from the group consisting of gold, the platinum group metals and mixtures thereof, which is included in the metal sulfide containing material. This metal sulfide-containing material is contacted with the manganese-containing ore at conditions effective to at least partially liberate the second metal from the material. The second metal is then recovered from the material.

The present contacting step results in a very desirable combination of events, e.g., chemically reducing, and preferably solubilizing, manganese; solubilizing metal from the metal sulfide; and at least partially liberating at least one first metal, and preferably at least one second metal. Effective first, and preferably second, metal recoveries are achieved. All this can be accomplished utilizing low grade (heretofore difficult to process) reducible manganese-containing ores and relatively inexpensive, plentiful metal sulfide-containing materials. Further the present process does not require the addition of sulfur dioxide or hydrogen sulfide to maintain or culture any bacteria.

The process of this invention is useful on any suitable first metal, reducible manganese-containing ore, e.g., an ore containing oxidized manganese. At least a portion of the manganese included in this ore should be chemically reducible in the present contacting step. Particularly, the process is useful on silver, manganese-containing ores in which at least a portion of the silver is locked by the manganese such that at least a portion of the silver is not readily recovered using conventional techniques, e.g., cyanide extraction. Such silver, manganese-containing ores are "preconditioned" in the present contacting step so that at least a portion, preferably a major portion, of the silver is liberated from the ore. By "liberated from the ore" is meant that the first metal (silver) in the ore after the present contacting can be more effectively recovered using conventional (cyanide extraction) processing relative to the uncontacted ore. In the process of this invention, a metal sulfide-containing material is contacted with the manganese-containing ore. In embodiments of the present invention in which the presence of Thiobacillus ferrooxidans is optional, the metal sulfide is preferably pyrites selected from a group consisting of iron pyrites, chalcopyrite, arsenopyrite, pyrrhotite, marcosite, stannite and mixtures thereof. More preferably, the metal sulfide comprises iron pyrites.

In embodiments of the invention which require the presence of Thiobacillus ferrooxidans any suitable metal sulfide capable of performing at the conditions of the present contacting step, and preferably capable of being oxidized by the bacteria, may be used. Because of cost, availability and performance considerations, the preferred metal sulfide for use in these embodiments is iron sulfide, in particular iron pyrites.

The amount of metal sulfide employed in the present contacting step should be sufficient to provide the chemical reduction/solubilization/liberation to the desired degree. Preferably, the amount of metal sulfide employed should be about 40% to about 120% of that required to achieve the desired degree of manganese chemical reduction for metal liberation. Substantial excesses of metal sulfides should be avoided since such excesses may result in materials separation and handling problems, and may even result in reduced recovery of the desired metal or metals. The metal sulfide component which is used in the process of this invention may be any metallic sulfide ore, including arsenic, zinc, iron, cobalt, nickel, tin, lead, and copper. The metal sulfide may be in any size or form. The metal sulfide component may be intermixed with the manganese-containing ore or brought in contact with the manganese-containing ore by the aqueous, acidic composition which is in turn intermixed with the manganese-containing ore. Metal sulfide components useful in this invention may include other minerals or compounds in amounts which do not substantially interfere or deleteriously affect the present process.

One embodiment of the invention involves the use of a metal sulfide-containing material which also includes one or more valuable second metals, such as gold, the platinum group meals and mixtures thereof. When such valuble second metal, in particular gold, is present, the present contacting step provides for at least partially liberating the second metal or metals from the sulfide-containing material, i.e., the second metal or metals are more effectively recovered from the material after the contacting relative to the uncontacted material. This material containing the desired second metal or metals, after contacting according to the present invention, is subjected to additional processing during which the second metal or metals are recovered from the contacted material.

Any suitable aqueous, acidic composition may be employed in the present process. The pH of the composition should be acidic and may vary depending, for example, on the composition of the ore or ores being treated, the composition of the metal sulfide-containing material being employed, and the presence or absence of other entities during the contacting. Preferably, the pH of the aqueous, acidic composition is in the range of about 0.1 to about 5. However, if an effective amount of Thiobacillus ferrooxidans is present during the contacting, the preferred pH of the aqueous, acidic composition is in the range of about 1.5 to about 4.5, and more preferably about 3.0 and lower. Still more preferably, if an effective amount of the bacteria is present, the pH of the aqueous, acidic composition is in the range of about 2.0 to about 3.0, with excellent results obtained with a pH in the range of about 2.5 to about 3.0.

The pH of the aqueous, acidic composition may be adjusted or maintained during the contacting step, for example, by adding acid to the aqueous, acidic composition.

The aqueous, acidic composition comprises water, preferably a major amount of water. The composition is preferably substantially free of ions and other entities which have a substantial detrimental effect on the present process. Any suitable acid or combination of acids may be included in, or added to, this composition to provide the desired acidity. For example, hydrogen halides preferably hydrogen chloride, sulfurous acid, sulfuric acid metal salts which decompose (in the aqueous, acidic composition) to form such acids, mixtures thereof and the like may be employed. Because of cost, availability and performance considerations, sulfuric acid is preferred. Quantity and concentration of the aqueous, acidic composition may be selected in accordance with the requirements of any given ore to be treated and as may be found advantageous for any given mode applying the process in practice.

In one embodiment, the present contacting occurs in the presence of added ferric ion in an amount effective to facilitate the liberating of the first metal from the ore. The ferric ion may be added to the contacting step separately, e.g., as Fe₂ (SO₄)₃ and/or other compounds which produce the desired amount of ferric ion when combined with the present aqueous, acidic composition in the contacting step. In order to more effectively control the amount of ferric ion present and to provide improved contacting, it is preferred that the added ferric ion be combined with the aqueous, acidic composition prior to the present contacting step. The amount of added ferric ion used in the present process is typically minor, when compared to the amount of ore and metal sulfide-containing material used, and may vary depending on many factors, for example, the composition of the ore or ores and of the metal sulfide-containing material and the degree of first metal liberation desired. Preferably, the added ferric ion is present in an amount of at least 10 ppm. (by weight) of the aqueous, acidic composition. More preferably, the added ferric ion is present in an amount in the range of about 0.01% to about 1.0% by weight of the aqueous, acidic solution.

In one embodiment, the present contacting occurs in the presence of Thiobacillus ferrooxidans bacteria in an amount effective to facilitate the liberating of the first metal from the manganese-containing ore. Since the contacting preferably results in at least a portion of the manganese in the ore being dissolved in the aqueous, acidic composition and since the bacteria is preferably present in the acidic, aqueous composition, the bacteria are preferably tolerant (remain active) in such manganese-containing compositions. The aqueous, acidic compositions and the bacteria contained therein are maintained under regeneration conditions, i.e., at conditions conducive to the propagation of bacteria, during the contacting step.

As the contacting step progresses, the aqueous, acidic composition (the lixiviant solution) preferably becomes increasingly concentrated in dissolved manganese from the ore, in the form of manganese sulfate if sulfuric acid is employed. Above certain high concentrations of manganese, the buildup of manganese will in turn reduce the activity of the Thiobacillus ferrooxidans bacteria. In practice, the contacting step is controlled, particularly through its initial stage, to produce effective quantities of adequately manganese tolerant bacteria, for example and preferably, by controlling the ratio of ore or ores to metal sulfide-containing material to aqueous, acidic composition and/or the bleed rate of the manganese-containing aqueous, acidic composition to insure a safe buildup rate of manganese ions in the aqueous, acidic composition. By increasing the proportion of solids to liquid, the manganese buildup rate in the aqueous, acidic composition is increased and vice versa. The manganese concentration, the total dissolved solid, and the bacterial activity in the aqueous, acidic composition can be monitored on a periodic basis as an aid to process control.

In instances where it is not practicable or desirable to exercise the required degree of control of the contacting step throughout the period of time required for developing suitably tolerant bacteria and where, consequently, it is preferred to commence the contacting step with an adequate supply of suitably tolerant bacteria, cultures of such bacteria may be prepared by known methods. Normally, the Thiobacillus ferrooxidans bacteria can tolerate manganese in concentrations as high as 2.5 weight percent. In concentrations above 2.5 weight percent, the growth of the bacteria is slowed to a point at which bacteria become inactive. However, the bacteria can be and preferably are acclimated to higher concentrations of manganese ion by slowly increasing the manganese ion concentration level in the aqueous, acidic composition. By normal acclimation techniques, the manganese tolerance of the bacteria can be increased to greater than about 4 weight percent. The bacteria are preferably acclimated as much as is possible and cost effective. Alternately, Thiobacillus ferrooxidans bacteria may be acclimated to higher manganese levels using chemostate techniques operating in a continuous mode.

Sources of the Thiobacillus ferrooxidans bacteria useful in this invention include sources such as the American Type Culture Center and bacteria found to be naturally occurring in ore bodies. Of the Thiobacillus ferrooxidans bacteria available from the American Type Culture Center, cultures ATCC-14119, ATCC-19859, ATCC-21834, and ATCC-33020 have been used in the process of this invention. All of these cultures have been found to be satisfactory.

The pH necessary for the bacterial action may preferably be as low as about 1.5 and as high as about 4.5 for the Thiobacillus ferroxidans bacteria. However, if the bacteria are acclimated to a lower pH, the pH of the aqueous, acidic composition in the present contacting step may be adjusted accordingly.

The aqueous, acidic composition should be maintained at a temperature to provide for effective contacting. When the bacteria are employed, such temperature should be such as to not unduly inhibit the growth of or destroy the bacteria. In some instances, bacterial activity has been maintained at a temperature as high as 75 degrees C., though normal strains of the bacteria are best maintained at below about 60 degrees C. which is the preferred upper limit. While limited activity is still apparent at 5 degrees C., the preferred lower limit is about 15 degrees C. More preferably, for the bacteria participation, the contacting occurs at a temperature in the range of about 15 degrees C. to about 40 degrees C. Still more preferably, the contacting temperature is in the range of about 20 degrees C. to about 30 degrees C. Both the temperature extremes and the preferred temperature ranges may be adjusted if the bacteria are acclimated to different ranges.

The bacteria are typically cultivated with nitrogen, phosphorous and sulfate, or utilize naturally occurring nutrients. Any suitable combination of compounds or components containing these constituents may be used to culture the bacteria. Suitable compounds include ammonia, ammonium sulfate, ammonium phosphate, alkali acid phosphate mixtures thereof and the like. Preferably, magnesium is also included in the culturing compounds or components and suitable magnesium content may be provided by adding magnesium sulfate.

In utilizing the process of this invention, certain precautions should preferably be taken to improve performance. For example, the raw materials and equipment utilized throughout the processing circuit should normally be such as will not release or act as bactericides under the conditions prevailing during the process. Minerals which may be harmful to the bacteria include cobalt, zinc, nickel, copper, mercury, and molybdenum. Concentrations of these minerals found in pyrites normally do not exceed levels which would be harmful to the bacteria. Element concentrations which would be harmful to the bacteria are illustrated in Zitzchriferology Microbiology, 12/72, 310. However, as with the manganese, these concentrations may be exceeded by the use of bacteria which have been acclimated to the harmful mineral.

The action of the bacteria on iron pyrite may produce an effective addition of sulfuric acid to the aqueous, acidic composition during the contacting step. Without limiting this invention to any theory or chemical/physical mechanism, it is postulated that this reaction is as follows:

    2FeS.sub.2 +71/2O.sub.2 +H.sub.2 O→Fe.sub.2 (SO.sub.4).sub.3 +H.sub.2 SO.sub.4

In instances where the contacting step results in reducing the sulfuric acid content to the aqueous, acidic composition without a corresponding decrease in the ferric ion content, hydrolysis of the ferric sulfate is postulated to form sulfuric acid by the following reaction:

    6H.sub.2 O+Fe.sub.2 (SO.sub.4).sub.3 →3H.sub.2 SO.sub.4 +2Fe(OH).sub.3

This results in the precipitation of ferric salts. A controlled amount of oxygen, such as oxygen from air, is present in order to promote bacterial growth.

In order to utilize normal recovery techniques for the first metal (silver) content of an ore, the manganese content of the ore does not need to be reduced or eliminated. The first metal (silver) is at least partially liberated from the ore. In other words, the manganese is at least partially disassociated from the silver, and not necessarily removed from the ore. In order to disassociate the manganese from the first metal (silver), the manganese is preferably solubilized, for instance, as manganese sulfate. Desirably, the manganese sulfate may be removed from physical mixture with the first metal (silver) and redeposited within the ore such that the liquid effluent from the process is not overly laden with the manganese sulfate since this sulfate may be an environmental concern.

The present process may be conducted on a batch or continuous basis. The present contacting step may be conducted on a pad, with the ore or ores to be treated situated in a heap; or in a vat, tank or other suitable arrangement. The primary criterion for the contacting step is that the desired manganese chemical reduction/sulfide metal solubilization/first metal liberation takes place. Preferably, the first metal, manganese-containing ore and metal sulfide-containing material are brought together to form an intimate admixture generally with the aqueous, acidic composition. If bacteria are employed, it is preferred that this intimate admixture also include the bacteria. If bacteria are utilized, the aqueous, acidic composition preferably includes one or more nutrients useful by the bacteria. One or more of these nutrients may be included with one or more of the ore, sulfide material, intimate admixture and aqueous, acidic composition. Additional amounts of acid and/or ferric ion may be added during the contacting to provide the desired pH and ferric ion concentration.

The solid ore/material remaining after the contacting step may be subjected to any suitable metal recovery processing step or steps for the recovery of the first metal, e.g., silver, and the second metal, gold, the platinum group metals and the like. For example, this solid ore/material may be neutralized with any suitable basic material, such as white lime or milk of lime, and then subjected to a conventional sodium cyanide extraction, followed by activated carbon treatment and zinc dust precipitation. Alternately, the solid ore/material after contacting can be neutralized and subjected to an ammonium thiosulfate or an acid thiourea extraction followed by zinc dust precipitation. Still further, the solid ore/material after contacting can be subjected to a brine extraction followed by ion exchange to recover the desired metal or metals. The conditions at which these various recovery processing steps take place are conventional and well known in the art, and therefore are not described in detail here. However, it is important to note that conducting the metal recovery processing on the ore/material after the contacting of the present invention provides improved metal recovery performance relative to conducting the same metal recovery processing without this contacting.

One processing arrangement which provides outstanding results involves the agglomeration of the first metal, manganese-containing ore and the metal sulfide-containing material. The ore and material are preferably subjected to crushing, grinding, or the like processing to reduce particle size to that desired optimum metallurgical liberation, generally a maximum particle diameter of about 1/2 inch or less. The ore and material particles are mixed with sufficient aqueous acid (H₂ SO₄), and if desired, bacteria. This intimate admixture is formed into agglomerates by conventional processing, such as extruding, pilling, tableting and the like.

The agglomerates are placed on a pad, to form a heap which is built up by addition of agglomerates, preferably over a period of time in the range of about 15 days to about 60 days. During the time the heap is being built up, and preferably for a period of time ranging up to about 3 months, more preferably about 2 months to about 3 months after the last agglomerates are added to the heap, an aqueous, acidic (H₂ SO₄) composition is made to flow through the heap, e.g., from the top to the bottom of the heap. If bacteria are used, the aqueous, acidic composition includes one or more nutrients for the bacteria. After contacting the heap, the aqueous, acidic composition is collected and processed for disposal, processed for manganese and/or sulfide metal recovery, and/or recycled to the heap. This contacting provides another important benefit in that at least a portion of the cyanacides, such as copper, which may be present in the ore and/or metal sulfide-containing material is removed and/or deactivated. Such cyanacides cause substantial increases in cyanide consumption if present in cyanide extraction processing. Therefore, removing and/or deactivating cyanacides in the present contacting step provides for more effective metals recovery by cyanide extraction.

After the heap/aqueous, acidic composition contacting has proceeded to the desired extent, an aqueous basic (e.g., white lime, milk of lime or the like basic components) composition is contacted with the heap to neutralize the heap. After this neutralization, the agglomerates may be placed placed on a second heap, which is preferably larger than the heap previously described.

However, it is preferred that the neutralized agglomerates be broken apart and reagglomerated prior to being placed on the second heap. This can be done using conventional means, such as subjecting the agglomerates to grinding, milling or the like processing, and then forming the second agglomerates by extruding, tableting, pilling, pelletizing or the like processing.

In any event, if a second, preferably larger, heap is formed on a pad, and a dilute aqueous cyanide, preferably sodium cyanide, solution is made to contact the second heap. Typically, this cyanide contacting is performed in the presence of air. Preferably, the cyanide solution is percolated through the second heap. The cyanide solution, after being contacted with the second heap, contains silver (from the silver, manganese-containing ore) and possibly gold (from the metal sulfide-containing material). This solution is collected and sent to conventional further processing for recovery of silver and gold.

Both heaps are preferably maintained at ambient conditions e.g., of temperature and pressure. Also, both heaps may be built up and worked (contacted) with the aqueous, acidic composition and the cyanide solution for as long as the economics of the particular application involved remain favorable.

The following non-limiting Examples illustrate certain aspects of the present invention. However, these illustrations are not to be considered as limitations on the invention.

EXAMPLES 1 TO 12

These examples illustrate the use of iron pyrite at controlled pH conditions in the present invention.

A series of twelve (12) runs were made using differing amounts of iron pyrites and aqueous, acidic compositions of differing pH's to contact a silver, manganese-containing ore which contained 6.23 troy ounce per ton of silver, 1.8% by weight of iron and 9.7% by weight of reducible manganese (all calculated as elemental metal). The iron pyrites-containing material was obtained from Anaconda Minerals Company, Caribou Property, in New Brunswick Canada. The analysis of this iron pyrites-containing material was as set forth in the following Table 1.

                  TABLE 1                                                          ______________________________________                                         COMPONENT    WEIGHT PERCENTAGE                                                 ______________________________________                                         Fe           43.0        (A.A.)                                                S            40.3                                                              Insolubles   7.1                                                               Zn           1.3                                                               Pb           0.9                                                               Cu           0.2                                                               Al.sub.2 O.sub.3                                                                            0.6                                                               MgO          0.3                                                               Ag           1.0         troy ounce/ton                                        Au           0.03        troy ounce/ton                                        ______________________________________                                    

Mineralogically this material was primarily iron pyrites and pyrrotite with minor amounts of galena, sphalerite and chalcopyrite.

All the runs were conducted using de-ionized water and no bacteria were used in the study. One percent (weight per volume of aqueous, acidic composition (W/v)) of the ore and varying concentrations of pyrites were combined with aqueous, acidic compositions of varying pH's. The original acidity of the composition was derived from the inclusion of a proper amount of 2N of sulfuric acid. The pH in each run was adjusted daily to the designated value using 2N of sulfuric acid. The control runs (Examples 10, 11 and 12) were conducted identically except that no pyrite was included. All materials used in the runs were previously autoclaved to insure the sterility of the system. This autoclaving step was performed on the materials (except the bacteria) used in each of the following Examples. The combined mixtures were maintained at room temperature (about 22 degrees C.) and were shaken or agitated to provide adequate mixing. The relative amount of the total manganese available from the ore which was dissolved in the aqueous, acidic medium after 23 days was determined. These determinations were based on manganese analysis of the liquid using an inductively coupled plasma emission spectrometer. Results of these runs are shown in Table 2.

                  TABLE 2                                                          ______________________________________                                                         Pyrites     Relative                                                           Concentration                                                                              Amount of Total                                    Example pH      % (W/v)     Manganese Dissolved                                ______________________________________                                         1       0.5     0.2         15                                                 2       1.5     0.2         14.4                                               3       2.5     0.2         14.4                                               4       4       0.2         4.6                                                5       5       0.2         2                                                  6       6       0.2         1                                                  7       0.5     0.5         16                                                 8       1.5     0.5         15                                                 9       2.5     0.5         14.4                                               10      0.5     0           4                                                  11      1.5     0           2.4                                                12      2.5     0           1                                                  ______________________________________                                    

These results show that iron pyrites are effective to reduce and solubilize manganese from a silver, reducible manganese-containing ore. In each of Examples 1 to 9, the final aqueous, acidic composition also contained dissolved iron from the iron pyrites. The silver in the ore after the contacting was more susceptible to recovery, e.g., by conventional cyanide extraction, relative to that in the untreated ore. These results also show that the pH of the aqueous, acidic composition can influence the performance of the system.

EXAMPLES 13 TO 26

A culture of Thiobacillus ferrooxidans bacteria (ATCC33020) was grown under autotrophic conditions in shake flasks containing 10 liters of mineral medium. The medium contained KH₂ PO₄ (0.4 gr./l.), (NH₄)₂ SO₄ (0.8 gr./l.), MgSO₄.7H₂ O (0.16 gr./l.), and FeSO₄ (5 gr./l.). The pH of the medium was adjusted to and maintained at 2.5 using 1N of H₂ SO₄. The bacterial culture was shaken at 200 rpm at room temperature (about 22 degrees C.) to insure adequate aeration and mixing. Ferrous sulfate was the sole energy source for the growth of Thiobacillus ferrooxidans bacteria.

The bacteria, at late exponential phase of growth, were harvested by centrifugation. A pellet of the harvested bacteria was transferred and resuspended in a shake flask containing 100 ml. of the test solution. The pyrite test solution contained KH₂ PO₄ (0.4 gr./l.), (NH₄)₂ SO₄ (0.8 gr./l.), MgSO₄ (0.16 gr./l.), a designated concentration of 100 mesh pyrite material, and 1 percent (W/v) of 100 mesh silver, manganese-containing ore. The pyrite material and ore were as described in Examples 1 to 12. The flask was aerobically shaken at room temperature and at a speed of 200 rpm. The pH of the test solution was initially 2.5 with the inclusion of the appropriate amount of 2N of sulfuric acid. Depending upon the amount of pyrite used in the test solution, it was necessary, in some cases, to adjust the pH of the test solution to 2.5 with 2N of sulfuric acid.

A control solution was prepared in a similar way using an identical test solution, except that Thiobacillus ferrooxidans bacteria were not present.

Results of these tests showing the relative amount of manganese dissolved after 25 days are presented in Table 3.

                  TABLE 3                                                          ______________________________________                                                                  Relative Amount                                                 Pyrite Concentration                                                                          of total Manganese                                    Example   % (W/v)        Dissolved                                             ______________________________________                                         13        0              0.3                                                   14        0.05           8.0                                                   15        0.1            10.1                                                  16        0.3            14.1                                                  17        0.5            14.9                                                  18        1              14.1                                                  19        2              15.0                                                  20        0              0.3                                                   21        0.05           1.1                                                   22        0.1            1.4                                                   23        0.3            1.1                                                   24        0.5            1.1                                                   25        1              2.0                                                   26        2              1.7                                                   ______________________________________                                    

These results demonstrate the improved manganese reduction/solubilization achieved using a combination of certain metal sulfides and Thiobacillus ferrrooxidans. These results cannot be compared directly with the results from Examples 1 to 12 since different aqueous, acidic compositions were used in each set of runs. In each of Examples 14 to 19 and 21 to 26 the final aqueous, acidic composition also contained dissolved iron from the iron pyrites. The silver in the ore after each of these contactings (Examples 14 to 19 and 21 to 26) was more susceptible to recovery relative to the silver in the original, silver, manganese-containing ore.

EXAMPLES 27 AND 28

Examples 17 and 24 respectively, are repeated except that the aqueous, acidic composition contained ferric ion in the form of 0.5% (W/v) of ferric sulfate.

Results of these Examples after 25 days are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                                                  Relative Amount                                                 Pyrites Concentration                                                                         of Total Manganese                                    Example   % (W/v)        Dissolved                                             ______________________________________                                         27        0.5            13                                                    28        0.5            20                                                    ______________________________________                                    

The final aqueous, acidic compositions in each of Examples 27 and 28 contained iron from the iron pyrites. The silver in the ore after each of these contactings was more susceptible to recovery relative to the silver in the ore after Examples 17 and 24, respectively. These results indicate that the presence of added ferric ion, with or without the presence of Thiobacillus ferrooxidans is beneficial to facilitate the reduction/dissolution of manganese and facilitate the liberation of silver from a silver, manganese-containing ore.

Although not wanting the invention to be limited by any particular theory or mechanism, it is believed that the ferric ion can serve neither as an energy source for Thiobacillus ferrooxidans, nor as a reducing agent for manganese, but, in an acidic environment is an efficient leaching agent. It is postulated that the ferric ion reacts with the iron sulfide/pyrites to generate ferrous ion which is used in the biological or chemical reduction/dissolution of manganese.

EXAMPLES 29 to 32

Examples 15, 17, 22 and 24 were repeated except that FeS was substituted for the pyrites. Results of these Examples, compared with the results of Examples 15, 17, 22 and 24, are shown in Table 5.

                  TABLE 5                                                          ______________________________________                                                                         Relative                                               Pyrites     FeS         Amount of Total                                        Concentration                                                                              Concentration                                                                              Manganese                                      Example % (W/v)     % (W/v)     Dissolved                                      ______________________________________                                         15      0.1         --          10.1                                           29      --          0.1         4.0                                            17      0.5         --          14.9                                           30      --          0.5         6.8                                            22      0.1         --          1.4                                            31      --          0.1         1.4                                            24      0.5         --          1.1                                            32      --          0.5         1.4                                            ______________________________________                                    

These results demonstrate that metal sulfides, such as FeS, in combination with Thiobacillus ferrooxidans are effective to reduce manganese, and at least partially liberate silver from a silver, manganese-containing ore. These results further demonstrate the superiority of the pyrites/bacteria combination relative to the FeS/bacteria combination in the present process.

EXAMPLES 33 TO 36

These Examples illustrate the present process for the recovery of (1) silver from a silver, manganese-containing ore and (2) gold from a gold, iron-pyrites-containing ore.

Thiobacillus ferrooxidans bacteria was cultivated and harvested as in Examples 13 to 26.

The bacteria, at late exponential phase growth, were harvested by centrifiguration. A pellet of the harvested bacteria was transferred and resuspended in a shake flask containing 10 liters of the test solution. The test solution contained KH₂ PO₄ (0.4 gr./l.), (NH₄)₂ SO₄ (0.8 gr./l.), MgSO₄ (0.16 gr./l.), 60 gr. of the respective 100 mesh gold, iron pyrites-containing ore from two locations--designated Pyrite Ore 1 and Pyrite Ore 2, respectively and 200 gr. of the silver, manganese-containing ore described previously. Both Pyrite Ores 1 and 2 include gold in an amount such that it would be economically attractive to recover the gold. The iron pyrites in the Pyrite Ores 1 and 2 reduces the economic attractiveness of such gold recovery, and it would be advantageous to liberate at least a portion of the gold from the gold, pyrite ores before the ores are subjected to gold recovery processing.

The flask, containing the above-noted components was aerobically shaken at room temperature and at a speed of 200 rpm for 41 days. The pH of the test solution was initially 2.5 using 2N of sulfuric acid and the pH was adjusted, as necessary, to 2.5 with 2N of sulfuric acid.

A control solution was prepared in a similar way using an identical test solution, except that Thiobacillus ferrooxidans bacteria were not present.

After 41 days, the relative amount of manganese dissolved in each of the test solutions was determined. Results of these determinations are shown in Table 6.

                  TABLE 6                                                          ______________________________________                                                                    Relative Amount of                                  Example                                                                               Pyrite Ore                                                                               Bacteria  Total Manganese Dissolved                           ______________________________________                                         33     1         No        12.2                                                34     1         Yes       13.4                                                35     2         No        12.8                                                36     2         Yes       12.8                                                ______________________________________                                    

These results show that iron pyrites, with and without Thiobacillus ferrooxidans, is effective to reduce and solubilize manganese from a silver, manganese-containing ore. In each of Examples 33 to 36, the final aqueous, acidic composition, the test solution, also contained dissolved iron from the iron pyrite. The silver in the ore after the contacting was more responsive to recovery, e.g., by conventional cyanide extraction, relative to that in the untreated ore.

The remaining solid, containing gold and silver, from each of runs noted above was centrifuged, washed, dried and then subjected to a laboratory cyanide extraction for gold recovery. This laboratory extraction is known to provide results which are reasonably correlatable to results obtained in commercial cyanide extraction operations. The amount of total gold extracted for each of the Examples is shown in Table 7.

                  TABLE 7                                                          ______________________________________                                         Example Pyrite Ore Bacteria  % of Gold Extracted                               ______________________________________                                         33      1          No        26.2                                              34      1          Yes       93.1                                              35      2          No        65.2                                              36      2          Yes       80.2                                              ______________________________________                                    

The amount of gold extracted in each of Examples 33 to 36 is increased relative to the amount of gold that can be recovered from Pyrite Ore 1 and 2, respectively, without the above-noted treatment.

These results indicate that manganese, silver-containing ore, with and without Thiobacillus ferrooxidans, is effective to at least partially liberate gold from a gold, pyrite-containing ore. The presence of the bacteria does provide for substantially improved gold recoveries. This is surprising since the amounts of manganese dissolved would appear not to be substantially affected by the presence of bacteria. This indicates that the reduction or dissolving of manganese by itself does not necessarily relate to the degree of total silver/gold liberation from the ores by the above processes. In other words, this makes clear that the chemical reduction of manganese and the liberation of silver/gold from the ore by the process of this invention are unexpected and distinct.

While the present invention has been described with respect to various specific examples and embodiments, it is to be understood that the present invention is not limited thereto and that it can be variously practiced within the scope of the following claims. 

The embodiments of the present invention in which an exclusive property or privilege is claimed are as follows:
 1. A process for recovering silver from an ore containing manganese comprising: contacting said ore with an aqueous, acidic composition and a material containing at least one metal sulfide in the presence of ferric ion at conditions effective to (1) chemically reduce manganese, (2) solubilize metal from said metal sulfide in said acidic, aqueous composition, and (3) liberate silver from said ore; and recovering silver from said ore.
 2. The process of claim 1 wherein said contacting occurs in the presence of added ferric ion.
 3. The process of claim 2 wherein said sulfide is iron pyrites.
 4. The process of claim 2 wherein said material further includes at least one second metal selected from the group consisting of gold, the platinum group metals and mixtures thereof; said contacting occurs at conditions effective to liberate second metal from said material; and said process further comprises recovering said second metal from said material.
 5. The process of claim 4 wherein said second metal is gold.
 6. The process of claim 2 wherein the pH of said aqueous, acidic composition is in the range of about 0.5 to about 5.0 and said aqueous, acidic composition contains sulfuric acid.
 7. The process of claim 2 wherein said sulfide has a formula of (Me)y Sx wherein x is greater than y and Me is a metal selected from the group consisting of Fe, Mo, As, Cu, Co, Ni, Sn, Sb, Bi, Pb, Zn and mixtures thereof.
 8. The process of claim 7 wherein said contacting occurs in the presence of oxygen.
 9. The process of claim 2 wherein said sulfide includes at least one sulfur to sulfur bond.
 10. The process of claim 9 wherein said contacting occurs in the presence of oxygen.
 11. The process of claim 2 wherein said contacting occurs in the presence of oxygen.
 12. The process of claim 2 wherein said ore and said material are agglomerated and the resulting agglomerates are placed to form a first heap which is contacted with said aqueous, acidic composition.
 13. The process of claim 1 wherein the pH of said aqueous, acidic composition is in the range of about 0.5 to about 5.0 and said aqueous, acidic composition contains sulfuric acid.
 14. The process of claim 13 wherein said sulfide has a formula of (Me)y Sx wherein x is greater than y and Me is a metal selected from the group consisting of Fe, Mo, As, Cu, Co, Ni, Sn, Sb, Bi, Pb, Zn and mixtures thereof.
 15. The process of claim 13 wherein said sulfide includes at least one sulfur to sulfur bond.
 16. The process of claim 13 wherein said contacting occurs in the presence of oxygen.
 17. The process of claim 1 wherein asid contacting occurs in presence of Thiobacillus ferrooxidans.
 18. The process of claim 1 wherein said material further includes at least one second metal selected from the group consisting of gold, the platinum group metals and mixtures thereof; said contacting occurs at conditions effective to liberate second metal from said material; and said process further comprises recovering said second metal from said material.
 19. The process of claim 18 wherein said second metal is gold.
 20. The process of claim 1 wherein said ore and said material are agglomerated and the resulting agglomerates are placed to form a first heap which is contacted with said aqueous, acidic composition.
 21. The process of claim 20 wherein said agglomerates after said contacting are reagglomerated and placed on a second heap which is contacted with aqueous cyanide solution to solubilize silver from said ore.
 22. The process of claim 12 wherein said agglomerates after said contacting are reagglomerated and placed on a second heap which is contacted with aqueous cyanide solution to solubilize silver from said ore.
 23. The process of claim 1 wherein said sulfide has a formula of (Me)y Sx wherein x is greater than y and Me is a metal selected from the group consisting of Fe, Mo, As, Cu, Co, Ni, Sn, Sb, Bi, Pb, Zn and mixtures thereof.
 24. The process of claim 23 wherein said sulfide includes at least one sulfur to sulfur bond.
 25. The process of claim 23 wherein said contacting occurs in the presence of oxygen.
 26. The process of claim 1 wherein said sulfide includes at least one sulfur to sulfur bond.
 27. The process of claim 1 wherein said contacting occurs in the presence of oxygen.
 28. A process for recovering silver from an ore containing manganese comprising: contacting said ore with an aqueous, acidic composition and a material containing at least one metal sulfide in the presence of ferric ion at conditions effective to (1) chemically reduce manganese, (2) solubilize metal from said metal sulfide in said aqueous, acidic composition, and (3) liberate silver from said ore, provided that said contacting occurs in the presence of Thiobacillus ferrooxidans; and recovering silver from said ore.
 29. The process of claim 28 wherein said metal sulfide is iron sulfide and said contacting occurs in the presence of oxygen.
 30. The process of claim 24 wherein said contacting occurs in the presence of added ferric ion.
 31. The process of claim 30 wherein the pH of said aqueous, acidic composition is in the range of about 3.0 and lower and said aqueous, acidic composition contains sulfuric acid.
 32. The process of claim 28 wherein said contacting occurs in the presence of added ferric ion.
 33. The process of claim 32 wherein said contacting occurs in the presence of oxygen.
 34. The process of claim 28 wherein the pH of said aqueous, acidic composition is in the range of about 1.5 to about 4.5.
 35. The process of claim 28 wherein the pH of said aqeous, acidic composition is in the range of about 3.0 and lower and said aqueous, acidic composition contains sulfuric acid.
 36. The process of claim 28 wherein said material further includes at least one second metal selected from the group consisting of gold, the platinum group metals and mixtures thereof; said contacting occurs at conditions effective to liberate second metal from said material; and said process further comprises recovering said second metal from said material.
 37. The process of claim 28 wherein said ore, said material and said Thiobacillus ferrooxidans are agglomerated and the resulting agglomerates are placed to form a first heap which is contacted with said aqueous, acidic composition.
 38. The process of claim 37 wherein said agglomerates after said contacting are reagglomerated and placed on a second heap which is contacted with aqueous cyanide solution to solubilize silver from said ore.
 39. The process of claim 28 wherein said sulfide includes at least one sulfur to sulfur bond.
 40. The process of claim 39 wherein said contacting occurs in the presence of oxygen.
 41. The process of claim 28 wherein said contacting occurs in the presence of oxygen. 